1. Field of the Invention
The present invention generally relates to a brake system and method for a DC brush motor. More specifically, the present invention relates to a brake system and method for a DC brush motor without a Hall sensor.
2. Description of the Related Art
A conventional brush-less motor control system acquires a frequency generator signal directly from an installed Hall sensor or through an external chip using three-phase control signal. A decrease to zero voltage of the frequency generator signal represents the motor having come to a stop. On the other hand, brush motors with Hall devices characterized by easy control and generating feedback signals used to be prevailed but cannot meet the requirement of cost reduction. This creates a big demand of DC motors of simpler structures without Hall devices. However, many problems emerged as a result of the application with the motors. One of them is concerning the braking of the motor.
Ordinarily, there are two ways to brake a motor. First way is to stop providing current to the motor immediately, so that the motor loses energy and drags to a stop. But, it takes much time to make a complete stop and fails to meet the requirements of use in some applications. Second way is to provide the motor with a reverse current. Therefore, a greater deceleration is applied to complete the brake operation quickly. However, in a DC motor system without frequency generator signals feedback, it cannot be easily detected if the motor is in the stationary state. Moreover, it may result in advancing the brake operation, or even over-braking to cause the motor reversed according to the amount of the load.
FIG. 1 is a block diagram of a conventional brush-less DC motor with a Hall sensor. Referring to FIG. 1, the conventional brush-less DC motor system 100 with a Hall sensor directly detects and feedbacks the rotating speed of the motor. The processing unit 101 drives a DC brush-less motor 103 through a motor driver 102. As the motor 103 starts to rotate, the frequency generator signal is generated by the motor driver 102 and then provided to the processing unit 101 for rotating speed control and brake control. However, a prohibitive cost and sophisticated circuitry are characteristic of the system 100.
U.S. Patent Pub. No. 20040022153 (Shen) discloses a rotating speed control apparatus and method for a DC motor without a Hall sensor, by detecting the armature current of the motor and then calculating coefficients and rotating speed of the motor. The compatibility of this method is poor because it needs to use different mathematic operations for motor coefficients with different motors. Besides, it also uses a differential amplifier to calculate the armature current, but there are still problems with resistor matching and noise interference. Therefore, the calculated armature currents are prone to errors. Accordingly, coefficients and rotating speed of the motor derived from substituting the calculated armature currents into equations are even less accurate. Moreover, the method is used to calculate coefficients and rotating speed of the motor, but doesn't disclose how to perform the brake control.